WO2006062124A1 - Exhaust gas purification device - Google Patents

Abstract

An exhaust gas purification device constructed to reduce and purify NOx by having a NOx storage and reduction catalyst (5) installed in the middle of an exhaust gas flow path (2, 4). A fuel reforming catalyst structure (7) or a plasma fuel reforming means (8) for resolving fuel into H2 and CO is installed on the upstream side of the NOx storage and reduction catalyst (5) in the exhaust gas flow path (2, 4). The fuel is dissolved into H2 and CO, NOx on the surface of the NOx storage and reduction catalyst is efficiently reduced into N2 by the H2 and CO. A high NOx reduction rate is always achieved despite varying operating conditions.

Description

 Specification

 Exhaust purification equipment

 Technical field

 The present invention relates to an exhaust purification device.

 Background art

 [0002] Conventionally, exhaust purification has been attempted with an exhaust purification catalyst installed in the middle of an exhaust pipe, and this type of exhaust purification catalyst has a lean exhaust fuel ratio. NOx in the exhaust gas is oxidized and temporarily stored in the form of nitrate, reducing the O concentration in the exhaust gas.

 2 NOx storage and reduction catalysts are known that have the property of decomposing and releasing NOx through the intervention of unburned HC, CO, etc.

[0003] As this type of NOx occlusion reduction catalyst, platinum 'barium' alumina catalyst, platinum 'power lithium / alumina catalyst and the like are already known as having the above-mentioned properties.

[0004] Then, if the NOx storage amount increases and reaches the saturation amount, no more NOx can be stored in the NOx storage reduction catalyst. It is necessary to decompose and release NOx by reducing the O concentration of the exhaust gas entering.

 2

 [0005] For example, when used in a gasoline engine, by reducing the operating air-fuel ratio of the engine (operating the engine at a rich air-fuel ratio), the O concentration in the exhaust gas is reduced and the exhaust gas

 2

 It is possible to promote the decomposition and release of NOx by increasing the reducing components such as unburned HC and CO. However, if the NOx storage reduction catalyst is used as an exhaust purification device of a diesel engine, the engine is operated at a rich air-fuel ratio. It is difficult to drive.

[0006] Therefore, a means for adding fuel (HC) to the exhaust gas upstream of the NOx storage reduction catalyst is newly provided, and the added fuel is used as a reducing agent on the NOx storage reduction catalyst.

 React the NOx storage and reduction catalyst by actively reducing the O concentration in the exhaust gas.

 2

 It is necessary to plan.

 Patent Document 1: Japanese Unexamined Patent Publication No. 2000-356127

 Disclosure of the invention

Problems to be solved by the invention [0007] In this manner, in the method of adding fuel upstream of the NOx storage reduction catalyst in this way, part of the HC generated by evaporation of the added fuel is exhaust gas on the surface of the NOx storage reduction catalyst. The oxygen concentration in the atmosphere surrounding the NOx storage and reduction catalyst

 2 2 Since the decomposition and release of force NOx starts almost at zero, the combustion temperature (approximately 220 to 250) required for HC to react (combust) with O on the surface of the NOx storage-reduction catalyst ° C)

 2

 However, under operating conditions (for example, heavy traffic congestion, slow driving in Tokyo, etc.), NOx cannot be efficiently decomposed and released from the NOx storage reduction catalyst, and the regeneration of the NOx storage reduction catalyst is efficient. Insufficient progress resulted in a problem that the storage capacity declined as the recovery rate of NOx storage sites in the catalyst volume decreased.

[0008] The present invention has been made in view of the above circumstances, and provides an exhaust purification device that can always obtain a high NOx reduction rate regardless of operating conditions, or a relatively low temperature range. The purpose is to provide an exhaust purification system that can achieve a high NOx reduction rate.

 Means for solving the problem

[0009] According to a first aspect of the present invention, the present invention provides an exhaust purification device configured to reduce and purify NOx by providing a NOx storage reduction catalyst in the middle of an exhaust passage. , A fuel reforming means for decomposing the fuel into H and CO upstream of the NOx storage reduction catalyst in the exhaust passage (

 2

 A fuel reforming catalyst structure or plasma fuel reforming means) is provided.

[0010] According to a second aspect of the present invention, in the first aspect, the present invention is the one in which the plasma generating means for oxidizing NO to NO is disposed upstream of the fuel reforming means in the exhaust passage.

 2

 It is.

 [0011] According to a third aspect of the present invention, in the second aspect, the present invention provides the plasma generating means, wherein the exhaust gas ratio is lean and the NOx is reduced by NO to NO when the exhaust fuel ratio is lean.

 2

 It is controlled to promote the warehouse.

[0012] According to a fourth aspect of the present invention, the fuel reforming means according to the first aspect is characterized in that the fuel reforming means decomposes the fuel into H and CO when the air-fuel ratio is rich, and reduces the NOx of the NOx storage reduction catalyst. reduction

 2

 We are controlled to do so.

[0013] According to a fifth aspect of the present invention, in the first aspect, the fuel reforming means comprises: When the exhaust gas temperature is sufficiently high, the fuel is supplied without decomposition, and the fuel is instantly concentrated.

 [0014] According to the sixth aspect of the present invention, the present invention provides a NOx occlusion reduction catalyst installed in an exhaust pipe for introducing exhaust gas from an engine car, and an unreduced agent as a reducing agent during regeneration of the NOx occlusion reduction catalyst. A fuel injection control device that controls fuel injection of the engine so that a large amount of fuel can be left in the exhaust gas, and discharge into the exhaust gas upstream of the NOx storage reduction catalyst to generate plasma, and the plasma does not A plasma generator that breaks down the fuel into H and CO

 2

 It is equipped with.

 [0015] According to a seventh aspect of the present invention, in the sixth aspect, the present invention further comprises a fuel addition device so that fuel can be added directly to the exhaust pipe upstream of the plasma generator. is there.

 [0016] According to the first aspect of the present invention, H and CO can be decomposed by the fuel reforming means.

 2 2 and CO efficiently reduce NOx on the surface of the NOx storage reduction catalyst to N

 2

 As a result, a high NOx reduction rate can always be obtained regardless of various operating conditions. In addition, the fuel is decomposed into H and CO by the fuel reforming means, and the ratio of the highly reactive H and CO is increased.

 twenty two

 Since the NOx reduction rate can be obtained from a relatively low temperature range, for example, there is a lot of traffic congestion! ヽ The exhaust temperature is low at low loads, such as slow driving in cities!易 Easy to continue operating conditions ヽ Even under operating conditions, NOx contained in exhaust gas discharged outside the vehicle can be more effectively reduced than before.

[0017] According to the second aspect of the present invention, when the plasma generating means for oxidizing NO into N 2 O is arranged upstream of the fuel reforming means in the exhaust passage, the plasma generating means relates to the temperature.

2

 NO can be oxidized to NO, making it easy to store NOx by NOx storage reduction catalyst.

 2

 be able to.

 [0018] According to the third aspect of the present invention, when the plasma generating means is controlled to oxidize NO to NO and promote NOx occlusion by the NOx occlusion reduction catalyst when the exhaust fuel ratio is lean,

2

 NOx occlusion by the Ox occlusion reduction catalyst can be further facilitated.

[0019] According to the fourth aspect of the present invention, the fuel reforming means may convert the fuel to H when the air-fuel ratio is rich in fuel.

 2

If it is controlled to decompose into CO and reduce NOx in the NOx storage reduction catalyst, H and CO To reduce NOx on the surface of the NOx storage reduction catalyst to N more efficiently.

 2

 it can.

 [0020] According to the fifth aspect of the present invention, when the fuel reforming means is controlled so that the fuel is supplied without being decomposed and the fuel is instantly concentrated when the exhaust temperature is sufficiently high, NOx occlusion reduction NOx on the surface of the catalyst can be appropriately reduced to N.

 2

 [0021] In the sixth aspect of the present invention, when the fuel injection control device controls fuel injection into each cylinder of the engine to leave a large amount of unburned fuel in the exhaust gas, the unburned fuel is absorbed by NOx. It will be led together with the exhaust gas as a reducing agent for the storage reduction catalyst.

 [0022] When the exhaust gas containing a large amount of unburned fuel is discharged by the plasma generator in the previous stage, the unburned fuel (HC) in the exhaust gas is decomposed into H and CO by a partial acid-acid reaction by the plasma.

 2

 Therefore, highly reactive H and CO on the surface of the NOx storage reduction catalyst in the latter stage

 2

 It is lower than the combustion temperature of HC and reacts (combusts) with O in the exhaust gas from the combustion temperature.

 2

 [0023] Thus, in the sixth aspect of the present invention, the O concentration in the atmosphere around the NOx storage-reduction catalyst becomes almost zero and the decomposition and release of NOx is started, and the NOx absorption is continued as it is.

 2

 NOx is efficiently reduced to N by highly reactive H and CO on the surface of the storage reduction catalyst

 As a result, it is possible to obtain a higher NOx reduction rate in a relatively low temperature range than when HC produced from unburned fuel is directly reacted on the NOx storage reduction catalyst.

[0024] Further, in the seventh aspect of the present invention, an additional fuel addition device may be provided so that fuel can be added directly to the exhaust pipe upstream of the plasma generation device. Accordingly, it is possible to add the fuel directly into the exhaust pipe by the fuel addition device, and to realize the reducing atmosphere necessary for the regeneration of the NOx storage reduction catalyst more reliably.

 The invention's effect

 [0025] According to the first aspect of the present invention described above up to the fifth aspect, NO which is related to temperature can be oxidized to NO, or the fuel can be decomposed into H and CO. Reduction rate

twenty two

 If you can get it!

[0026] According to the sixth aspect and the seventh aspect of the present invention described above, fuel addition is performed by controlling the fuel injection into each cylinder on the engine side to leave a large amount of unburned fuel in the exhaust gas. The unburned fuel (HC) in the exhaust gas is discharged from the plasma generator in the previous stage. Decomposes into H and CO by Zuma, and is relatively low by these highly reactive H and CO

twenty two

High NOx reduction rate can be obtained from the temperature range, so it is easy to continue the operation state with low load and low exhaust temperature, such as heavy traffic, slow driving in Tokyo, etc. Even so, NOx contained in the exhaust gas discharged outside the vehicle can be reduced more effectively than before, and the practicality of exhaust purification equipment using NOx storage reduction catalyst is greatly improved. If it can, it can have an excellent effect.

Brief Description of Drawings

FIG. 1 is a schematic view showing a case where a fuel reforming catalyst structure is used in an embodiment of the present invention.

 FIG. 2 is a schematic view showing a case where a plasma fuel reforming means is used in an embodiment of the present invention.

 FIG. 3 is a schematic view showing a fuel reforming catalyst structure of the present invention.

FIG. 4 is a schematic view showing a plasma fuel reforming means of the present invention.

FIG. 5 is a schematic view showing another embodiment of the present invention.

 FIG. 6 is a graph showing the relationship between the NOx reduction rate and the catalyst temperature together with a comparative example.

FIG. 7 is a graph showing the relationship between NOx reduction rate and load together with a comparative example.

Explanation of symbols

 2 Exhaust manifold (exhaust flow path)

 4 Exhaust pipe (exhaust flow path)

 5 NOx storage reduction catalyst

 7 Fuel reforming catalyst structure (fuel reforming means)

 8 Plasma fuel reforming means (fuel reforming means)

 29 Plasma generation means

 41 Diesole Engine (Engine)

 43 exhaust gas

 44 Exhaust pipe

 45 NOx storage reduction catalyst

47 Plasma generator 54 Control device (fuel injection control device)

 55 Fuel injector

 55a Fuel injection signal

 61 Fuel addition equipment

 BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

 FIG. 1 to FIG. 4 are examples of embodiments in which the present invention is implemented using a NOx occlusion reduction catalyst, in which exhaust gas 3 discharged from a diesel engine 1 through an exhaust manifold 2 circulates. In the middle of the exhaust pipe 4, a NOx occlusion reduction catalyst 5 having a flow-through type honeycomb structure is provided by being held in a casing 6.

 [0031] A fuel reforming means, that is, a fuel reforming catalyst structure 7 or a plasma fuel reforming means 8 is provided upstream of the casing 6 in the exhaust pipe 4.

 Here, as a preferred example of the fuel reforming catalyst structure 7, the fuel reforming catalyst structure 7 as shown in FIGS. 1 and 3 has an introduction pipe 9 and an exhaust pipe 10 leading to the exhaust pipe 4. A fuel reformer 12 that forms an internal space 11, a fuel reforming catalyst 13 installed in the fuel reformer 12, and fuel from the upstream side to the internal space 11 of the fuel reformer 12 A fuel addition nozzle 14 for opening and closing, an introduction valve 15 for opening and closing the introduction pipe 9, and a discharge valve 16 for opening and closing the discharge pipe 10.

 [0033] On the other hand, as a preferred example of the plasma fuel reforming means 8, the plasma fuel reforming means 8 as shown in FIGS. 2 and 4 includes a plasma fuel reformer 17 that leads to the exhaust pipe 4, and The plasma fuel reformer 17 includes a high-voltage power source 18 that applies a voltage to the plasma fuel reformer 17, and the plasma fuel reformer 17 forms an internal space 19 that leads to the exhaust pipe 4 and a discharge unit 20 that serves as a ground electrode, and a discharge An introduction portion 22 that forms a mixed gas flow path 21 so as to guide a fuel gas mixture of fuel such as light oil and air to the internal space 19 of the portion 20, and an insulator portion 23 disposed between the discharge portion 20 and the introduction portion 22 And a high voltage electrode 24 supported by the introduction part 22. In the figure, reference numeral 25 denotes a cooling water flow path for cooling the discharge part 20, and 26 denotes a fixing bolt for fixing the discharge part 20 and the introduction part 22. Further, the discharge part 20 may be an insulator without using the end part 20a on the high voltage electrode 24 side as a ground electrode.

[0034] Fuel reforming means in the exhaust pipe 4 (fuel reforming catalyst structure 7 or plasma fuel reforming means On the upstream side of 8), a plasma generator 27 consisting of a pair of plate electrodes opposed to each other in the exhaust pipe 4 as shown in FIGS. 1 and 2, and a high voltage for applying a voltage to the plasma generator 27 A plasma generating means 29 equipped with a power source 28 and is provided.

[0035] The diesel engine 1 is equipped with a rotation sensor 30 for detecting the engine rotation speed. The rotation speed signal 30a from the rotation sensor 30 and the accelerator sensor 31 (detects the depression angle of the accelerator pedal). The load signal 31a from the sensor and the temperature signal 32a from the temperature sensor 32 installed in the exhaust pipe 4 are input to the control device 33.

On the other hand, in the control device 33, the amount of N Ox generated based on the current operation state determined from the rotation speed signal 30a from the rotation sensor 30 and the load signal 31a from the accelerator sensor 31 is determined. The estimated NOx generation amount, the temperature signal 32a from the temperature sensor 32, the fuel reforming means (fuel reforming catalyst structure 7 or plasma fuel reforming means 8), and plasma The generation means 29 is controlled. Here, the control device 33 may receive signals from other sensor forces and control the fuel reforming means and the plasma generating means 29.

 [0037] In Fig. 1 and Fig. 2, 34 denotes a turbocharger, 35 denotes an intake pipe, and 36 denotes an intercooler.

 [0038] The operation of the embodiment of the present invention will be described below.

 [0039] In various operating states, when the amount of NOx generated from the rotation sensor 30 and the accelerator sensor 31 is estimated and the temperature is detected by the temperature sensor 32, the control device 33 appropriately controls the control signal to the plasma generation means 29. 28a is sent to control the plasma generating means 29, and in the case of the fuel reforming catalyst structure 7, the control device 33 sends control signals 9a and 10a to the fuel reforming catalyst structure 7 to add the fuel addition nozzle 14 In the case of the plasma fuel reforming means 8, the control device 33 sends a control signal 18a to the plasma fuel reforming means 8 to control the amount of fuel added. And controls the supply of high-voltage power 18.

[0040] Next, in the plasma generation means 29, a high voltage is applied to the flat plate plasma generator 27 by the high voltage power supply 28 to generate plasma in the exhaust pipe 4 and is affected by temperature. NO in the exhaust gas 3 is oxidized to NO.

 2

 [0041] The fuel reforming catalyst structure 7 controls the amount of fuel added to the fuel reformer 12, controls the temperature, controls the generation of H and CO generated by the fuel reforming catalyst 13, and exhausts the fuel.

 2

 Supply into gas 3. The plasma fuel reforming means 8 generates a plasma in the internal space 19 by applying a high voltage to the high-voltage electrode 24 from the high-voltage power source 18, and generates fuel in the internal space 19 that is not affected by temperature. And reformed into CO and reformed gas (water

 2

 Gas) is supplied into the exhaust gas 3.

[0042] Here, when the exhaust fuel ratio is lean, the plasma generating means 29 is operated by the control signal 28a from the control device 33, and the NOx is reduced to NO and the NOx occlusion reduction catalyst 5

 2

 When the air-fuel ratio when reducing NOx is fuel rich, the fuel reforming means (fuel reforming catalyst structure 7 or plasma fuel) is controlled by the control signals 9a, 10a, 18a from the control device 33. The reforming means 8) is activated, the fuel is decomposed into H and CO, and the exhaust gas 3

 2

 And NOx occluded in the NOx occlusion reduction catalyst 5 is efficiently reduced.

[0043] Further, when the exhaust temperature is sufficiently high (350 ° C or higher), the control device 33 does not process the fuel reforming catalyst 13 of the fuel reforming catalyst structure 7 or the plasma fuel reforming means 8 The fuel without applying high voltage to the high voltage electrode 24 may flow down and supplied without decomposition, and the fuel may be enriched instantaneously as a rich spike, and the NOx stored in the NOx storage reduction catalyst 5 may be reduced. .

 Therefore, according to the embodiment of the present invention, it can be decomposed into H and CO by the fuel reforming means (fuel reforming catalyst structure 7 or plasma fuel reforming means 8). NOx storage

 twenty two

 NOx on the surface of the reduction catalyst 5 is efficiently reduced to N, resulting in various operating conditions.

 2

 A high NOx reduction rate can always be obtained regardless of the situation.

[0045] Further, the fuel is decomposed into H and CO by the fuel reforming means, and the highly reactive H and CO are used.

 twenty two

 It is possible to obtain a relatively low and high NOx reduction rate from the temperature range.For example, the exhaust temperature is low at low loads, such as in a congested winter, slow driving in a metropolitan area, etc., and the operating state continues. Even under operating conditions that are likely to occur, NOx contained in the exhaust gas discharged outside the vehicle can be reduced more effectively than before.

[0046] In the embodiment of the present invention, NO is converted to NO on the upstream side of the fuel reforming means in the exhaust passage. If the plasma generating means 29 to be converted is arranged, the NOx storage / reduction catalyst 5 facilitates NOx storage because the plasma generating means 29 can oxidize NO to NO regardless of the temperature.

 2

 be able to.

 [0047] In the embodiment of the present invention, the plasma generating means 29 is controlled by the control device 33 to promote NOx occlusion by the NOx occlusion reduction catalyst 5 by oxidizing NO to NO when the exhaust fuel ratio is lean.

 2

 If controlled to do so, NOx occlusion by the NOx occlusion reduction catalyst 5 can be further facilitated.

 [0048] In the embodiment of the present invention, the fuel reforming means is controlled by the control device 33 so as to reduce the NOx of the NOx occlusion reduction catalyst 5 by decomposing the fuel into H and CO when the air-fuel ratio is the fuel rich.

 2

 If NO, NOx on the surface of the NOx occlusion reduction catalyst 5 is more efficiently N by H and CO.

 2 2 can be reduced.

[0049] In the embodiment of the present invention, the fuel reforming means supplies the fuel non-decomposingly and enriches the fuel instantaneously when the exhaust gas temperature is sufficiently high (above 350 ° C) by the control device 33. If controlled so, NOx on the surface of the NOx occlusion reduction catalyst 5 can be appropriately reduced to N.

 2

 it can.

 Hereinafter, another embodiment of the present invention will be described with reference to the drawings.

 FIGS. 5 to 7 show another embodiment of the present invention. In the exhaust emission control device of this embodiment as shown in FIG. 5, the exhaust gas is discharged from the diesel engine 41 through the exhaust manifold 42. In the middle of the exhaust pipe 44 through which the exhaust gas 43 circulates, a NOx occlusion reduction catalyst 45 having a flow-through type H-cam structure is held and installed in a casing 46. Is equipped with a plasma generator 47 that discharges into the exhaust gas 43 to generate plasma.

 [0052] This plasma generator 47 has a force that allows the electrodes 48 and 49 to face each other and discharge between each other. The distance between the electrodes 48 and 49 can be set almost uniformly. If so, various shapes such as a plate shape, a rod shape, and a cylindrical shape can be employed.

[0053] Further, each of the electrodes 48, 49 has a structure in which a power source 51 is connected via an inverter 50. In particular, in this embodiment, a vehicle-mounted battery is assumed as the power source 51. AC high voltage of appropriate voltage and frequency that can be discharged by inverter 50 is applied to each electrode 48, 4 9 can be applied.

 Further, the accelerator of the driver's seat (not shown) is provided with an accelerator sensor 52 (load sensor) that detects the accelerator opening as a load of the diesel engine 41, and at the appropriate position of the diesel engine 41. A rotation sensor 53 for detecting the rotation speed is provided, and the accelerator opening signal 52a and the rotation speed signal 53a from the acceleration sensor 52 and the rotation sensor 53 constitute an engine control computer (ECU: Electronic Control Unit). This is input to the control device 54 (fuel injection control device).

 [0055] On the other hand, in the control device 54, in accordance with the current operating state determined from the accelerator opening signal 52a and the rotational speed signal 53a, the fuel is injected toward the fuel injection device 55 that injects fuel into each cylinder. A fuel injection signal 55a for commanding the injection timing and the injection amount is output.

 Here, the fuel injection device 55 is constituted by a plurality of injectors (not shown) provided for each cylinder, and the electromagnetic valves of these injectors are supplied by a fuel injection signal 55a from the control device 54. The valve opening control is performed to control the fuel injection timing and injection amount (valve opening time).

 However, in this embodiment, the control device 54 determines the fuel injection signal 55a in the normal mode based on the accelerator opening signal 52a and the rotational speed signal 53a. When the mode is switched from the normal mode to the regeneration mode at regular intervals, the fuel is injected near the compression top dead center (crank angle 0 °), which is later than the compression top dead center. One or more post injections will be executed at non-ignition timing (starting time is in the range of crank angle 90 ° to 120 °)!

 That is, when the boost injection is performed at the non-ignition timing later than the compression top dead center following the main injection in this way, unburned fuel (mainly HC: carbonization) in the exhaust gas 43 by this post injection. Hydrogen) will be added, and HC generated by this unburned fuel will be introduced as a reducing agent to the NOx occlusion reduction catalyst 45.

[0059] When the control device 54 determines that the exhaust gas temperature is low based on the accelerator opening signal 52a and the rotation speed signal 53a, the inverter of the plasma generator 47 A discharge command signal 50a is output to 50, and the discharge command signal 50a is received. Further, the plasma generator 47 is operated by the inverter 50 so that the discharge gas 43 is discharged.

[0060] Further, an injection nozzle 56 is provided through the exhaust pipe 44 upstream of the plasma generating device 47, and the light oil supply pipe 58 connects between the injection nozzle 56 and the light oil tank 57. The light oil (fuel as the reducing agent) in the light oil tank 57 is discharged through the injection nozzle 56 by the drive of the supply pump 59 installed in the middle of the light oil supply pipe 58 and the opening operation of the light oil injection valve 60. The fuel injection device 61 is composed of the injection nozzle 56, the light oil tank 57, the light oil supply pipe 58, the supply pump 59, and the light oil injection valve 60.

 [0061] Then, a drive command signal 59a to the supply pump 59 and a valve opening command signal 60a to the light oil injection valve 60, which are output from the control device 54 as necessary, are used to assist the fuel addition device 61. Fuel addition will be carried out.

 Accordingly, the fuel injection control in the control device 54 is periodically switched from the normal mode to the regeneration mode, and is delayed from the compression top dead center following the main injection of fuel performed near the compression top dead center. When post-injection is executed at the non-ignition timing, a large amount of unburned fuel (mainly HC: hydrocarbon) remains in the exhaust gas 43 due to this post-injection, and the reducing agent to the unburned fuel power NOx occlusion reduction catalyst 45 Will be guided with the exhaust gas 43.

 [0063] When the exhaust gas 43 containing a large amount of unburned fuel is discharged by the plasma generator 47 in the previous stage, the unburned fuel (HC) in the exhaust gas 43 is converted into H and CO by a partial acid-oxidation reaction by the plasma.

 H2 is highly reactive on the surface of the NOx storage reduction catalyst 45 in the latter stage.

 2

Combustion temperature power where CO is lower than the combustion temperature of conventional HC Reaction with O in exhaust gas 43 (combustion)

 2

 To do.

 [0064] As a result, the O concentration in the atmosphere around the NOx storage reduction catalyst 45 becomes almost zero.

 2

 As a result, decomposition and release of NOx is started, and NOx is reduced to N efficiently by the highly reactive H and CO on the surface of the NOx occlusion reduction catalyst 45.

 twenty two

 Compared with the case where the produced HC is reacted as it is on the NOx storage reduction catalyst 45, a relatively low V and high NOx reduction rate can be obtained from the temperature range.

[0065] In particular, in this embodiment, the exhaust pipe 44 on the upstream side of the plasma generator 47 is lightly connected. Since the fuel addition device 61 is additionally provided so that the oil can be directly added, the fuel addition device 61 can add the fuel directly into the exhaust pipe 44 as needed. The reducing atmosphere necessary for the regeneration of the storage reduction catalyst 45 will be realized more reliably.

[0066] Therefore, according to such embodiments described above, executes a post injection following the main injection by controlling the fuel injection into each cylinder in the diesel engine 41 side, exhaust gas ⁴³ in this post-injection Fuel is added by leaving a large amount of unburned fuel inside, and unburned fuel (HC) in the exhaust gas 43 is decomposed into H and CO by the plasma generator 47 in the previous stage,

 2

 High responsiveness, relatively low due to H and CO, high from the temperature range! NOx reduction rate can be obtained

 2

 So, for example, there is a lot of traffic !, low exhaust temperature at low load, such as slow driving in the city, etc. 43 NOx contained in 43 can be reduced more effectively than before, and the practicality of an exhaust purification device using the NOx storage reduction catalyst 45 can be greatly improved.

[0067] In fact, according to the results of experiments conducted by the present inventor, cases A and H in which HC produced from the added fuel as shown in the graph of FIG. The

 2

Case B, which was reacted on NOx storage-reduction catalyst 45, and Case C, where CO was reacted on NOx storage-reduction catalyst 45, were compared. Case C was lower than Case A, and higher in the temperature range. It has been confirmed that a reduction rate can be obtained, and furthermore, Case B has a higher NOx reduction rate from a lower temperature range than Case C. In the graph of Fig. 6, the vertical axis represents the NOx reduction rate, and the horizontal axis represents the catalyst temperature.

 [0068] Further, as shown in FIG. 7, the case X in which the unburned fuel is added in the apparatus configuration of the present embodiment described earlier, and only the NOx occlusion reduction catalyst 45 without the plasma generator 47 are provided. Compared with case Y, which is equipped and added with unburned fuel, case X has a higher NOx reduction rate than case Y in a lower load range (lower exhaust temperature! Operating range). It has been confirmed. The vertical axis in the graph of FIG. 7 indicates the NOx reduction rate, and the horizontal axis indicates the load of the diesel engine 41.

[0069] It should be noted that the exhaust emission control device of the present invention performs post injection at a non-ignition timing later than the compression top dead center following main injection, which is not limited to the above-described embodiment. In addition to leaving a large amount of unburned fuel, it is possible to leave a lot of unburned fuel (HC) by delaying or accelerating the injection timing of the main injection itself, and other points of the present invention. Of course, various changes can be made without departing from the scope.

Claims

The scope of the claims  [1] An exhaust gas purification apparatus configured to reduce and purify NOx by installing a NOx storage reduction catalyst in the middle of an exhaust flow path, and a fuel upstream of the NOx storage reduction catalyst in the exhaust flow path Exhaust gas purification equipment provided with fuel reforming means that decomposes H into CO.  2  [2] Generation of plasma that oxidizes NO to NO upstream of the fuel reforming means in the exhaust passage  2  The exhaust emission control device according to claim 1, wherein means are arranged. [3] The plasma generation means oxidizes NO to NO when the exhaust fuel ratio is lean, and stores NOx.  2  The exhaust emission control device according to claim 2, controlled to promote NOx occlusion by the original catalyst. [4] The fuel reforming means decomposes the fuel into H and CO when the air-fuel ratio is rich, and stores NOx.  2  2. The exhaust emission control device according to claim 1, which is controlled to reduce NOx of the original catalyst. [5] The exhaust emission control device according to [1], wherein the fuel reforming means is controlled to supply the fuel without decomposition when the exhaust gas temperature is sufficiently high so that the fuel is enriched instantaneously. [6] A NOx occlusion reduction catalyst installed in an exhaust pipe for leading exhaust gas from the engine, and the fuel injection of the engine so that a large amount of unburned fuel can be left in the exhaust gas as a reducing agent when the NOx occlusion reduction catalyst is regenerated. And a plasma generator for generating plasma by discharging into the exhaust gas upstream of the NOx storage reduction catalyst and decomposing unburned fuel into H and CO by the plasma. Exhaust gas purification equipment consisting of  2  7. The exhaust emission control device according to claim 6, further comprising a fuel addition device so that fuel can be added directly to the exhaust pipe upstream of the plasma generation device.